8.8 W diode-cladding-pumped Tm3+,Ho3+-dopedfluoride fibre laser

A maximum output power of 8.8 W was generated from a diode pumped Tm³⁺,Ho³⁺-doped ZBLAN glass fibre laser. The laser operated with a maximum slope efficiency of 36% with respect to the incident pump power. The wavelength was measured to be 2056 nm and some instability was observed in the output     

Er3+-Yb3+ and Er3+ doped fiberlasers

Single-mode fiber lasers operating at ~1.57 μm are described. Output powers of >2 mW are reported for laser diode pumped operation. Direct comparison is made between fiber lasers using sensitized erbium (Er³⁺ and Yb³⁺) and erbium on its own. The performance of Er³⁺-Yb³⁺ fiber lasers is analyzed in more detail as a function of fiber length. Both CW and Q-switched operations are studied and the results obtained demonstrate that practical sources at 1.5 μm are available from diode pumped Er³⁺ -Yb³⁺ systems     

Photon avalanche upconversion in Er3+:YAlO3

The results of an investigation of photon avalanche upconversion pumping in Er³⁺:TiAlO₃ are reported. Five pump wavelengths corresponding to transitions from the metastable ⁴I_13/2 state to the ²H_11/2 state generated upconversion laser emission at 549.8 nm. The dependence of the laser output power on pump power near laser threshold is discussed in terms of a four-level kinetics model and is shown to reflect the threshold power requirement for photon avalanche. The maximum output power at 7 K was 33 mW, giving an optical conversion efficiency of 3.5% and a conversion efficiency of 28% based on absorbed power. Pumping Er:YALO by cross relaxation energy transfer produced 166 mW of laser output with an optical conversion efficiency of 17%     

Gain measurement and upconversion analysis in Tm3+, Ho3+ co-doped alumino-zirco-fluoride glass

The small signal gain coefficients were measured in Tm³⁺,Ho³⁺ co-doped alumino-zirco-fluoride glass. A gain of 15%/cm at 2.05 μm was obtained for pump power density of 42 kW/cm². The temperature increase of the glass was found to be more than 150 K with this pump power, which was estimated from a comparison between fluorescence intensities of Tm^{3+ 3} F₄-³H₆ and Ho^{3+ 5} I₇-⁵I₈. An upconversion rate constant of 12.5×10^-17 cm³ sec^-1 from a coupled (Tm^{3+ 3}F₄, Ho^{3+ 5}I₇) level to a coupled (Tm^{3+ 3}H₅, Ho^{3+ 5}I₆) level was determined by fitting the experimentally obtained gain coefficients to the calculated one which takes into consideration any temperature increase     

Flashlamp-pumped Cr3+:GSAG laser

Flashlamp-pumped vibronic lasing has been demonstrated at room temperature with the garnet Cr³⁺: GSAG. Continuous wavelength tuning was observed from 765 to 801 nm in preliminary experiments. An energy output of 110 mJ/pulse was obtained at 784 nm with a slope efficiency of 0.12 percent. Wavelength dependent gain and loss data are presented and are discussed with reference to Cr³⁺: GSGG measurements.     

Laser action from Ho3+, Er3+, and Tm3+in YAlO3

Laser action has been observed for the following rare-earth ions in YAlO3:Ho³⁺(sensitized with Er³⁺and Tm³⁺), Er³⁺, and Tm³⁺(sensitized with Er³⁺) at wavelengths of 2.123, 0.851, and 1.861 μm, respectively. Measurements of spectroscopic properties, fluorescence kinetics, and laser performance of these ions in YAlO3are reported.     

Continuous-wave laser action in Er3+:YLF at 3.41 μm

Continuous-wave laser emission at 3.41 μm from an erbium-doped LiYF₄ crystal (Er³⁺:YLF) at 77 K is demonstrated. Operation of this four-level laser is based on the Er^{3+ 4}F_9/2-⁴I_9/2 transition. An output power of 12 mW and a slope efficiency of 2% have been achieved     

CW radio-frequency excited white-light He-Cd+ laser

We report on the design and performance of a continuous-wave transverse capacitively coupled radio-frequency excited He-Cd⁺ laser, which is capable of simultaneously delivering stable, tens-milliwatt power output at the three primary spectral lines blue: (λ=441.6 nm), green (λ=533.7 nm and λ=537.8 nm), and red (λ=635.5 nm and λ=636.0 nm). Mixing these lines can result in the laser beam featured by a wide band of colors, including white color. The radio-frequency discharge, that excited the He-Cd mixture inside an alumina ceramic tube (400 mm length and 4 mm inner diameter) inserted into the fused silica tubing, operated between 400 mm long and 4 mm wide outer electrodes. Transformation of the radio-frequency discharge impedance to the 50-Ω output resistance of the radiofrequency generator and symmetrization of the radio-frequency voltage were performed by a special matching circuit. Under single-line operation the He-Cd⁺ laser output powers of 60 mW, 38 mW and 14 mW were obtained for the blue, green and red lines, respectively, at an input radio-frequency power of 400 W. Owing to the power interaction between the laser oscillations at red and green higher laser output powers in red and green are possible under multi-line operation. At optimum conditions the white-light laser output power of about 60 mW is obtainable from the laser tube of 40 cm active length. The rms noise-to-signal ratio (lower than 0.4%) of the laser output power of the radio-frequency excited He-Cd⁺ laser was comparable to that of hollow cathode He-Cd⁺ lasers and much lower than that of conventional positive column He-Cd⁺ lasers. The presented laser has exhibited stable operation for more than 400 hours, showing ability to become a long life laser     

Spectroscopic Properties and Laser Performance of Er3+ and Yb3+ Co-Doped GdAl3(BO3)4 Crystal

An Er:Yb:GdAl₃(BO₃)₄ crystal was grown and room-temperature polarized absorption, emission, and gain spectra were investigated. Fluorescence decay curves of Er³⁺ at 1530 nm and Yb³⁺ at 1040 nm in the crystal were measured. Efficient laser operation of Er:Yb:GdAl₃(BO₃)₄ crystal at 1.5-1.6 mum was realized. Quasi-continuous-wave output powers of 1.8 W with slope efficiency of 19% and 0.78 W with slope efficiency of 14% were achieved in diode-pumped c-cut and c-cut and a-cut crystals, respectively. The output spectrum and polarization of Er:Yb:GdAl₃(BO₃)₄ laser were also investigated.     

Finite-element analysis of single-frequency silica-based Er3+-Yb3+ co-doped waveguide lasers

Continuous wave laser operations of silica-based Er³⁺-Yb³⁺ co-doped waveguides have been numerically analyzed by means of a finite-element method. The theoretical model, based on propagation-rate equations, describes uniform upconversion by a dipole-dipole interaction between Er³⁺ ions, and includes a pair-induced energy transfer process from Yb ³⁺-Er³⁺ Numerical results show that single-frequency operation with slope efficiency higher than 50% and threshold pump powers of few mW can be achieved in short and heavily doped waveguides equipped with input dielectric mirrors and output distributed Bragg reflectors     

Improved gain characteristics in high-concentrationEr3+/Yb3+ codoped glass waveguide amplifiers

High-concentration Er³⁺/Yb³⁺ codoped glass waveguide amplifiers are analyzed by means of a finite-element-based code. Efficient Yb³⁺ to Er³⁺ energy transfer is shown to be a useful mechanism to reduce performance degradation due to Er³⁺ ion-ion interactions. Numerical calculations based on realistic waveguide parameters demonstrate the possibility of achieving high gain with a short device length     

Anomalous dispersion in Er3+ and Yb3+-dopedfibers

In experimental and theoretical study of anomalous dispersion in Er³⁺and Er³⁺-Yb³⁺-doped fibers has been developed. Anomalous time delay caused by both absorption and emission at 1.535 μm has been theoretically calculated and experimentally measured. A pump power dependence of anomalous time delay in rare-earth-doped fibers has been theoretically calculated and experimentally investigated. It has been shown that pump power fluctuations lead to propagation time jitter in Er³⁺-doped fiber amplifiers. The pulse interaction due to refractive index change caused by gain saturation is predicted. It has been shown that for Er ³⁺-doped fibers with SiO₂-GeO₂ core composition, the anomalous dispersion per 1-dB gain is twice that of fibers with SiO₂-Al₂O₃ core, which is caused by gain curve form difference. A scheme of mutual compensation of intrinsic fiber dispersion and anomalous dispersion caused by Er³⁺ in the region 1.532-1.537 μm has been suggested     

Fluorescence dynamics of Er3+ and Ho3+ ionsand energy transfer in some fluoride glasses

A detailed study at room temperature of the fluorescence dynamics of Er³⁺ and Ho³⁺ ions and energy transfer processes Er³⁺→Ho³⁺ in the ABLA, BATY, and BIZYT fluoride glasses is reported. Numerous concentrations and different selective laser excitations in the visible and infrared spectral ranges are used. The best concentrations and the more suitable glasses for laser applications at 2 μm are determined     

Doubly Passively Self-Q-Switched Cr4+:Nd3+:YAG Laser With a GaAs Output Coupler in a Short Cavity

By using a GaAs as both an output coupler and a saturable absorber, we present a doubly passively self-Q-switched Cr⁴⁺:Nd³⁺:YAG laser in a short cavity for the first time to our knowledge. This laser can generate more symmetric pulse shape and shorter pulsewidth in comparison with the solely self-Q-switched Cr⁴⁺:Nd³⁺:YAG laser. The output pulse energy and peak powers are higher than those in our previous doubly passively Q-switched lasers. By considering the Gaussian spatial distribution of the intra-cavity photon density and the free carrier absorption (FCA) in GaAs wafer, a set of modified rate equations have been introduced to describe the performances of the doubly Q-switched Cr ⁴⁺:Nd³⁺:YAG laser with GaAs coupler. The numerical solutions of the equations and the experimental results are found to agree with each other very well. The effect of FCA process in GaAs wafer has been discussed and proved to play an important role in the pulse compression and symmetry     

Infrared cross-section measurements for crystals doped withEr3+, Tm3+, and Ho3+

The absorption and emission cross sections of the transition between the ground spin-orbit multiplet and the lowest excited multiplet were measured for Er³⁺, Tm³⁺, and Ho³⁺ ions in a variety of crystalline hosts. The materials that were investigated include LiYF₄, BaY₂F₈, Y ₃Al₅O₁₂, LaF₃, KCaF₃ , YAlO₃, and La₂Be₂O₅. The absolute magnitudes of the emission cross sections were determined from the absorption spectra, with the aid of the principle of reciprocity. The calculated radiative emission lifetimes derived from these measured cross sections agree well with the measured emission decay times for most materials. The potential use of these rare-earth-doped materials in pulsed laser applications requires that the ground state exhibit adequate splitting to minimize the detrimental effects of the ground state thermal population, and also that the emission cross section be sufficiently large to permit efficient extraction energy. The systems based on Ho³⁺ in the eightfold coordinated sites of LiYF₄, BaY₂F₈, and Y₃Al₅O₁₂ appear to be the most promising     

Average-power scaling of self-heated Sr+ afterglowrecombination lasers

The performance of a large-bore (25-mm) self-heated Sr⁺ (430.5-nm) recombination laser with longitudinal excitation is discussed in relation to the prospects for scaling average output power to the 5-10-W regime. Average-power scaling is found to be limited in large-bore laser tubes by slow interpulse thermal relaxation in the laser gas mixture with strong radial gradients in species' densities and temperatures at only modest pulse repetition frequencies, leading to premature termination of the population inversion on the tube axis. Proposals for circumventing these limitations in order to permit generation of multiwatt average laser output power at 430.5 nm from Sr ⁺ are discussed     

Self-Q-switched Nd3+: YAG and ruby lasers

Self-Q-switched operation of Nd³⁺: YAG lasers at 77°K and ruby lasers at 300 and 77°K pumped by the 5145-Å output of a pulsed argon ion laser is described. Self-Q-switched operation was obtained 1) by static mirror misalignment and 2) by static misalignment of the filament of the pumped laser material with respect to the mirror resonator axis. An output that consisted of a single giant pulse could be obtained for ruby by either method; for Nd³⁺: YAG, the output always consisted of one or more giant pulses and characteristic relaxation oscillations.     

Cr3+→Nd3+ energy transfer and Nd3+ laser action studies of La3Ga5SiO14:Cr3+,Nd3+ co-doped crystal

Energy transfer between Cr³⁺ and Nd³⁺ ions has been investigated in the 4.2-300-K temperature range by using steady-state and site-selective time-resolved laser spectroscopy. Radiative and nonradiative energy transfer has been studied from the time-resolved emission spectra and the donor fluorescence decays. The transfer efficiency was calculated as a function of temperature by using the Cr³⁺ lifetimes of the single doped and co-doped samples. Laser experiments were carried out in a diffusive cavity by pumping a co-doped rod 54 mm long and 5 mm in diameter with xenon flashlamps. The laser spectral emission shows a complex structure which varies as a function of pump energy. The temporal evolution of the laser spectrum is discussed in terms of a simple four-level spectral rate-equation laser model which takes into account the existence of two main broad Nd³⁺ site distributions with a large spectral overlap     

Efficient silica-based Ho3+ fibre laser for 2 μmspectral region pumped at 1.15 μm

For the first time an Ho³⁺ silica fibre laser has been realised using a Bragg grating as the input coupler and a fibre pump source at 1.15 μm. The output power of 280 mW at 2 μm is to the authors' knowledge the highest value reported so far for Ho³⁺ silica fibre lasers